Machine type communication (MTC) uses devices that capture certain events such as temperature, and gas or water consumption, and the like, and then send data over a wired or wireless network to an MTC application. Smart meters with metering application are expected to be one among the early MTC devices deployed. Many other MTC devices such as e-health monitors are envisioned and are expected to be widely used in the near future.
The 3GPP communication standards established common and specific service requirements including MTC communication scenarios. According to those standards, MTC devices may communicate directly with one or more MTC servers. In another communication scenario, so called local-access devices without 3GPP communication capability may be located in a MTC capillary network which provides local connectivity between the local-access devices within its coverage and a MTC gateway device. The MTC gateway device is a MTC device which acts as a gateway for local-access devices in a MTC capillary network to communicate through a public land mobile network (PLMN) with one or more MTC servers.
With regard to user equipment (UE) terminals running multiple “always-on” applications, the always-on applications must regularly send keep-alive packets to the application server to maintain the state of such persistent connections.
In general, radio resource scheduling refers to the process of dividing and allocating resources to specific UEs within a cell for the transmission and reception of data. The scheduling decisions cover not only the resource block assignments but also which modulation and channel-coding schemes to use (e.g., link adaptation). In essence, link adaptation adapts the selection of modulation and channel-coding schemes to current channel conditions. This in turn determines the data rate or error probability of each link.
A Medium Access Control (MAC) scheduler in an eNodeB (eNB) is in charge of assigning both uplink and downlink radio resources. The downlink scheduling information is transmitted in the Physical Downlink Control Channel (PDCCH). Uplink scheduling grants are indicated to the UE by transmitting all relevant uplink scheduling information within the PDCCH.
Allocation could be changed dynamically once per subframe, that is once per millisecond (e.g., dynamic scheduling). Each allocation could be scheduled by L1/L2 control signaling and consumes signaling resources from PDCCH.
For services with small data payloads and regular packet arrivals, the control signaling required for dynamic scheduling might be disproportionally large relative to the amount of user data transmitted. To reduce the amount of L1/L2 control signaling or even get rid of it completely, LTE also supports persistent scheduling (in addition to dynamic scheduling). Persistent scheduling implies that radio resources as well as a fixed modulation and channel-coding scheme are allocated to a user for a given set of subframes and uplink resources are allocated without a designated PDCCH uplink grant. With persistent scheduling it is difficult to allocate or reserve suitable number of resources for every user and resource mismatch is unavoidable. This is due to predicting the number of required retransmissions and in turn to allocate the required resources for retransmissions. Also, packets larger than the predefined persistent resource occur occasionally. To cope with this issue semi-persistent scheduling was introduced. The principle of semi-persistent scheduling includes two parts: persistent scheduling for initial transmissions and dynamic scheduling for retransmissions. Semi-persistent scheduling may enable the above mentioned issues with persistent scheduling to be mitigated.
Current persistent/semi-persistent scheduling mechanisms are not designed for local-access devices located in a MTC capillary network which communicate simultaneously through a MTC gateway device with one or more MTC servers or UE terminals running multiple applications.